Optically clear diaphragm for an acoustic transducer and method for making same

ABSTRACT

The present disclosure relates to a diaphragm that may be used with a mechanical-to-acoustical transducer. The diaphragm may include a layer of optically clear film, a damping layer and another layer of optically clear film. The damping layer may be an adhesive. The diaphragm may also comprise two optically clear films, optionally including a damping layer, wherein the films indicate a desired coefficient of linear thermal expansion in one or both of the machine and transverse directions.

RELATED APPLICATION

The present application is a continuation application of U.S.nonprovisional application Ser. No. 12/399,840, filed Mar. 6, 2009, thecontent of which is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

This application is directed at an optically clear diaphragm that may beutilized in a mechanical-to-acoustical transducer for the purpose ofgenerating sound. The diaphragm is one that provides a desired dampingvalue over a selected frequency range and/or that exhibits a desiredcoefficient of linear thermal expansion (CLTE) and/or desired stiffnessto allow for a desired construction of the transducer frame. Suchcharacteristics may be supplied by a diaphragm which contains at leasttwo optically clear films optionally adhered to each other via a dampinglayer.

BACKGROUND OF THE INVENTION

Mechanical-to-acoustical transducers may have an actuator that may becoupled to an edge of a speaker membrane or diaphragm that may then beanchored and spaced from the actuator. Such a system may provide adiaphragm-type speaker where a display may be viewed through thespeaker. The actuators may be electromechanical, such aselectromagnetic, piezoelectric or electrostatic. Piezo actuators do notcreate a magnetic field that may then interfere with a display image andmay also be well suited to transform the high efficiency short lineartravel of the piezo motor into a high excursion, piston-equivalentdiaphragm movement.

One example of mechanical-to-acoustical transducer including an actuatorthat may be coupled to an edge of a diaphragm material is recited inU.S. Pat. No. 7,038,356. The use of a support and actuator that wasconfigured to be responsive to what was identified as surroundingconditions of, e.g., heat and/or humidity, is described in U.S.Publication No. 2006/0269087.

SUMMARY

In a first exemplary embodiment, the present disclosure relates to adiaphragm for use with a mechanical-to-acoustical transducer comprising:

(a) a layer of optically clear film;

(b) a damping layer;

(c) a layer of optically clear film;

wherein the diaphragm has a composite damping value of tan delta equalto or greater than 0.04 in the frequency range of 500 Hz to 2000 Hz at30° C., wherein the diaphragm has a total luminous transmittance ofequal to or greater than 75%.

In a second exemplary embodiment, the present disclosure relates to adiaphragm for use with a mechanical-to-acoustical transducer comprising:

(a) a layer of optically clear film;

(b) a damping layer;

(c) a layer of optically clear film;

wherein the damping layer has a damping value of tan delta that is equalto or greater than 0.1 at said frequency range from 500 Hz to 2000 Hz at30° C.

In a third exemplary embodiment, the present disclosure relates to adiaphragm for use with a mechanical-to-acoustical transducer comprisingat least two optically clear films, wherein said films indicate acoefficient of linear thermal expansion (CLTE) in one of the machinedirection and transverse direction equal to or below 50 μm/m/° C. whenmeasured at the temperature range of 20° C. to 50° C. and wherein thetotal luminous transmittance of said diaphragm is equal to or greaterthan 75%.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of one example of amechanical-to-acoustical transducer.

FIG. 2 is a cross-sectional view of one example of a two layer opticallyclear diaphragm containing one damping layer.

FIG. 3 is a cross-sectional view of one example of a laminated diaphragmwith one damping layer where the damping layer is outside the laminateneutral axis.

FIG. 4 illustrates a biaxially stretched polymer roll with machinedirection (MD) and transverse direction (TD) and a range of CLTE andmodulus (E) for each direction.

FIG. 5 illustrates one example of utilizing a relatively soft dampedadhesive versus utilizing a relatively stiff adhesive on a 24″ audiotransducer.

FIG. 6 provides a comparison of a laminated biaxially stretched PETversus a monolithic polycarbonate diaphragm on a 19″ audio transducer.

FIG. 7 is a cross-sectional view of one example of a three layeroptically clear diaphragm with two damping layers.

FIG. 8 provides a comparison of a diaphragm laminated from biaxiallystretched PET with a relatively stiff adhesive versus a monolithicpolycarbonate diaphragm on a 24″ audio transducer.

FIG. 9 illustrates one example of a hybrid speaker frame and diaphragmwith an orthotropic diaphragm matching the CLTE in each direction of theframe.

FIG. 10 illustrates one example of the construction of a laminateddiaphragm utilizing different orientations of orthotropic polymermaterial.

FIG. 11 is a plot of the coefficient of linear thermal expansion (CLTE)versus thickness for biaxially stretched PET.

FIG. 12 illustrates one example of an aligned orthotropic diaphragmwhich may be used to control spacing of modes.

DETAILED DESCRIPTION

A mechanical-to-acoustical transducer, coupled to a diaphragm, for thepurpose of producing audio sound, is disclosed in U.S. Pat. No.7,038,356 and U.S. Publication No. 2006/0269087, whose teachings areincorporated herein by reference. In one configuration, the transduceramounts to a piezo motor coupled to a diaphragm so that the excursion ofthe actuator is translated into a corresponding, mechanically amplifiedexcursions of the diaphragm. The diaphragm may be curved and whenoptically clear, can be mounted on a frame over a video display toprovide an audio speaker

When constructing an optically clear transducer in front of a videodisplay there may be a number of applicable design objectives. Forexample, one may desire to reproduce an audio signal with a relativelysmooth frequency response, with a relatively high speaker efficiency andwith relatively low acoustic distortion while at the same timeminimizing optical distortions of the image of the underlying videodisplay. One may also allow the surface to be coated with a desirableoptical coating, providing sufficient surface hardness, impact andscratch resistance for long term use and minimizing the production costof said transducer. Furthermore, one may want to choose the CLTE offrame and diaphragm to be relatively close to each other to minimizeunwanted distortions of the diaphragm when temperatures change. Thechoice of material type and construction of the diaphragm may be one ofthe decisions that determine how well a given design objective may beachieved. Other aspects are the design of the actuator, the curve shapeof the diaphragm, the attachment of the diaphragm to the transducerframe, the construction and the relative stiffness of the transducerframe as well as the design of the drive electronics.

Parameters that may now be considered in determining the usefulness of adiaphragm towards achieving one or more of the design objectives notedabove may include one or more of the following: its elastic andcompressive modulus, its density, its thickness, its stiffness, itsdamping, its coefficient of in-plane linear thermal expansion, itsoptical transparency and haze, its yellowness, its UV stability, itsimpact resistance and toughness, its hardness, its ability to be easilycoated with a wide range of optical coatings and its cost. There aremany types of optically clear materials available that might be used asa diaphragm; however they may not have desirable performance in one ormore of the above parameters at the same time. For example, manymaterials may not possess a desired internal damping property.

Accordingly, there has been a need for a diaphragm that possesses one ormore of the above referenced desirable properties while at the same timeproviding a relatively high degree of internal damping.

Attention is directed to FIG. 1 which is a cross-sectional view of oneexample of a mechanical-to-acoustical transducer 104 coupled to the edgeof a diaphragm 110. At 108 is a sealing element (sometimes also calledsurround in the art) and 106 may be, e.g., a video display. The frame isshown at 102 where the frame material preferably has an elastic modulusof not less than 30 GPa. Typically this may be achieved with a metal ora polymer, including a reinforced polymer (e.g. a polymer containinginorganic filler such as glass). Such materials may also have a CLTE ofequal to or less than 35 μm/m/° C., i.e. between 5 μm/m/° C. to 35μm/m/° C., including all values therein in 1.0 μm/m/° C. increments.

Furthermore, in order to reduce optical distortion due to changes oftemperature the CLTE of the diaphragm (110) may be configured to berelatively close to the CLTE of the frame. For example, the differenceshould be less than or equal to 20 μm/m/° C., preferably it should beless than or equal to 10 μm/m/° C. and even more preferably it should beless than or equal to 5 μm/m/° C. The CLTE of the diaphragm generallyshould be at or below 50 μm/m/° C., preferably at or below 40 μm/m/° C.and even more preferably at or below 35 μm/m/° C. Such CLTE is desirablypresent in both in-plane dimensions of the diaphragm.

It is worth pausing and noting that poly(ethylene terephtalate) (PET) onits own had been considered as a suitable diaphragm due to its relativestiffness and the feature that it is a relatively low cost material,together with the fact that it is also available with optical coatings.One problem was that as applied for use in a mechanical-to-acousticaltransducer where it was coupled to at least one edge, it was notavailable in the required combination of thickness and optical quality.In order to overcome this problem the above referenced laminationapproach was employed along with the use of a pressure sensitiveadhesive (PSA). It was then recognized that the PSA not only allowed forthe production of the laminate, but also could be configured to beoptically clear as well as also providing damping to the entirelaminate. With attention directed to FIG. 5, a comparison of a speakerfrequency response between one relative stiff adhesive (UV cured: E˜ 1GPa) and relatively soft, dampened PSA adhesive (E˜ 5 MPa)—both for PETlaminate (i.e. two layers of PET). As can be seen, the smoothness of thefrequency response was much improved in the range of 500 Hz to 2000 Hzdue to the use of a relatively well damped and soft PSA adhesive as alaminating material.

In a first embodiment illustrated in FIG. 2, an optically cleardiaphragm (210) may be constructed with at least two optically clearfilms (212, 216). Shown at 215 is the centerline of the damping layer214. The films 212 and 216 themselves may be suitable for use with themechanical-to-acoustical transducer but not provide, on their own, adesired amount of damping. However, the use of at least one layer of anoptically clear damped material (214) may therefore lead to a desireddamping characteristic for the entire diaphragm.

Or stated another way, the overall damping of the diaphragm is higherthan the damping that would otherwise be present in the absence of thedamping layer. Furthermore, the diaphragm herein may also be describedas containing at least two layers of optically clear film, and a dampinglayer therebetween wherein the damping layer provides a relativelyhigher damping value than the other two layers of film material. Inaddition, the diaphragm herein is one that may overlie all or a portionof a display that provides visual information (text and/or images) to aconsumer.

The damping layer may itself comprise an optically clear material, andas disclosed herein, may have a characteristic damping performance. Thedamping layer may provide adhesive as between the layers 212 and 216.Such adhesion may be created by the application of pressure and/or heat.Such adhesion may also be developed as a consequence of a chemicalreaction, e.g. polymerization of a liquid precursor. Such chemicalreaction may be the result of an energy input, such as heat or lightenergy (e.g. UV light).

Through a combination of thickness and elastic modulus control thediaphragm now may achieve sufficient flexural and compressive stiffnessto allow it to resist internal acoustic pressure within the transducerenclosure without loss of desired low frequency output due to diaphragmbreakup. There is no fundamental limit in the elastic modulus of thefilms that may now be used to form the diaphragm, however a higherelastic modulus may allow for better performance.

The diaphragm may be configured such that the diaphragm laminateconstruction (e.g. two layers of optically clear film bonded togetherwith an adhesive) provides a composite elastic modulus of equal to orgreater than 2.0 GPa. Moreover, at least one of the optically clearfilms used to construct this diaphragm may themselves have an elasticmodulus of equal to or greater than 2.0 GPA. More preferably, thediaphragm laminate construction and at least one of the clear films usedherein may provide a composite elastic modulus of greater than 3.0 GPa.The maximum elastic modulus for the clear films and/or the diaphragmlaminate construction is contemplated herein not to exceed 80 GPa.Accordingly, the diaphragm laminate construction herein may have acomposite elastic modulus of 2.0 GPa to 80 GPa, including all valuestherein, in 0.2 GPa increments.

The term “elastic modulus” herein may be understood as reference toYoung's modulus. It is denoted by the letter E and it is typicallymeasured in tension by the appropriate equipment (for example: TAInstruments Q800 Dynamic Mechanical Analyzer). In case of anisotropiccharacteristics of the film or diaphragm and in case no direction hasbeen specified the term “elastic modulus” may be understood as referenceto the average value of the Young's modulus for all in-plane directionsof the film or diaphragm under discussion.

The term “damping” in this disclosure (also called tan delta or usingthe symbol 6) is known to be the ratio of loss modulus (E′) to storagemodulus (E″). How damping may be measured depends on what is measured:for a monolithic sheet of film materials it is preferably measured intension with the appropriate equipment (example: TA Instruments Q800Dynamic Mechanical Analyzer), for the damping layer (for example arelatively soft damped adhesive) one might consider to measure dampingin extension but when used in a constrained layer damper configuration(as is the case here) it is preferably measured in a so called vibratingbeam test in the sandwich beam configuration (example: ASTM E-756-05) asthis better captures the behavior in shear. In this case the ratio ofthe shear values of loss and storage moduli are measured but it is wellunderstood in the art how to calculate between tensile and shear moduliwhen one also knows Poisson's ratio. Damping values for the compositelaminated diaphragms may be calculated using the mathematical relationsknown as RKU (Ross, Kerwin, Ungar) in the art and by using the moduliand damping values for the damping layers and non-damping layers asmeasured in the previously described methods.

In many cases the resonances of dynamic mechanical analyzer equipmentlimit the upper frequency at which damping and modulus can be measuredto a fairly low value. For example this limit is 200 Hz for the Q800Dynamic Mechanical Analyzer. For materials that exhibit viscoelasticproperties (which will include many of the optical films, damping layersand adhesives in the present disclosure) there often is observed to be atemperature-frequency equivalence whereupon modulus and damping may beextrapolated to a frequency higher than the machine limit through anappropriate relation developed by carefully fitting data at multiplefrequencies and temperatures. This temperature-frequency superpositiontechnique is well known in the art. For example, attention is directedto “The Handbook for Viscoelastic Vibration Damping” by David I. G.Jones, 2001, John Wiley & Sons Ltd.

Density in this disclosure (also known as mass density) may beunderstood as the ratio of mass/volume and is denoted by the symbol ρ.(may be measured for example according to ASTM D1505-03).

There is no limit for the thickness of the diaphragm as this may varyamongst other things with the diaphragm outer dimensions, the designintent and the intended use of a specific audio transducer and thediaphragm materials chosen. However, in a preferred embodiment thethickness of the diaphragm is in the range from 100 μm to 2 mm,including all values therein, in 10 μm increments. For example, onepreferred range is 100 μm to 1 mm. For the specific example of alaminate of two or more biaxially stretched PET films and a transducerto be used in conjunction with a 24″ class LCD display and intended foruse in a computer monitor, all-in-one PC or TV, a preferred thicknessrange is approximately 450 to 600 μm.

Preferably the diaphragm has a combination of relatively low compositedensity and relatively high composite elastic modulus as the thicknessand the density (ρ) together determine the mass of the diaphragm whichin turn may limit the high frequency output above the main systemresonance of the diaphragm and may contributes to the transducerefficiency. Furthermore, the ratio of E/ρ may influence the main systemresonance which a designer might want to place within a certainfrequency region depending on the design intent.

There is no specific limit in the density of the films and/or dampinglayer(s) (e.g. adhesives) that may be used to provide the diaphragmsherein. However a relatively lower density for any of the films ordamping layer(s) may allow for higher speaker efficiency. In a preferredimplementation at least one of the optically clear films themselves hasa density of less than or equal to 1500 kg/m³. In another preferredembodiment the diaphragm laminate (e.g. at least two layers of filmbonded with an adhesive as the damping layer) has a composite density ofless than 1500 kg/m³.

As alluded to above, at least two optically clear films may now belaminated together by at least one layer of an optically clear film thatprovides damping (preferably an adhesive) which then results in adiaphragm construction having an overall desired damping performance.Some of the benefits of this damping may include the reduction inresonances of the diaphragm, for example one-dimensional beam waves,and/or the reduction in acoustic distortion in general. In thisconstruction the damped adhesive may act as a constrained layer damper.Constrained layer damping is known in the art to work by sandwiching arelatively soft and damped compliant layer between two or morerelatively stiffer layers. As the laminate flexes the middle layer maybe sheared and the damping of the middle layer may destroy mechanicalenergy in the form of heat. Preferably the damping layer is placed asclose as is reasonably possible to the neutral axis of the laminate tomaximize the shearing. For the purpose of constructing the diaphragmsherein the damping layer may be selected such that it can be used as therelatively softer compliant layer in between relatively stiffer layersof the optically clear film.

In a preferred implementation the thickness, the damping tan delta, theelastic modulus as well as the location of the damping layer, which asnoted may preferably be an adhesive, may collectively contribute to,(along with the damping of any other films,) a composite damping tandelta δ of the diaphragm of at least 4% (δ>=0.04) throughout thefrequency range of 500 Hz to 2000 Hz and for a temperature of 30° C.More preferably the composite damping tan delta δ of the diaphragm is atleast 6% (δ>=0.06) throughout the frequency range of 500 Hz to 2000 Hzand for a temperature of 30° C. Even more preferably the compositedamping tan delta δ of the diaphragm is at least 8% (δ>=0.08) throughoutthe frequency range of 500 Hz to 2000 Hz and for a temperature of 30° C.Furthermore, the composite damping tan delta of the diaphragm may be inthe range of 0.04 to 0.5, including all values therein in increments of0.01, over the frequency range from 500 Hz to 2000 Hz at 30° C.

In addition, preferably the elastic modulus (E) of the damping layer isten times lower than the modulus of elasticity of any optically clearfilm(s) used as part of the diaphragm. That is, the elastic modulus ofthe damping layer (E_(DL)) may be 10% or less than the elastic modulusof any optically clear film (E_(Film)) used in the diaphragmconstruction, which may be written asE _(DL)≦(0.1)E _(Film).

Even more preferable is if is E_(DL) is at least one hundred times lowerthan the modulus of elasticity of any optically clear film used as partof the diaphragm, which may be written as:E _(DL)≦(0.01)E _(Film).

It is also preferable that the damping tan delta of the damping layer isat 0.1 or more (δ≧0.1) throughout the frequency range of 500 Hz to 2000Hz and at a temperature of 30° C. That is, it is contemplated that onemay provide a diaphragm with two or more optically clear film layers,and at least one damping layer, with the feature that at least onedamping layer on its own has a damping tan delta of 0.1 or more in thefrequency range from 500 Hz to 2000 Hz at 30° C. Even more preferablythe damping tan delta of the damping layer is at 0.2 or more throughoutthe frequency range of 500 Hz to 2000 Hz and at a temperature of 30° C.Furthermore, the damping tan delta of at least one damping layer may bein the range of 0.1 to 10 over the frequency range from 500 Hz to 2000Hz at 30° C., in 0.05 increments. Moreover, the damping value tan deltaof the damping layer may be at least 1.5 times as high as any of the tandelta damping values of the optically clear films.

Expanding upon this embodiment, one may therefore construct a diaphragmformed by three or more film layers with two or more damping layers.Again, the damping layers may be adhesive layers as noted above. In suchexample, the damping layers do not have to have the same mechanicalproperties, provided that at least one of the damping layers provides,as noted, a damping tan delta of 0.1 or more in the frequency range from500 Hz to 2000 Hz at 30° C. It shall be pointed out that the additionaldamping layer(s) may not provide any damping at all to the diaphragm andmay only provide adhesion between two optically clear films through anymeans.

Therefore, it may be appreciated that the present disclosurecontemplates a diaphragm construction containing a plurality of filmlayers and a plurality of damping layers, wherein at least one of thedamping layers has a damping tan delta of 0.1 or more in the frequencyrange from 500 Hz to 2000 Hz at 30° C., and the remaining damping layersmay have a damping tan delta of less than 0.1 at the same frequencyrange and temperature.

Furthermore, it is preferable if the center line of at least one layerof the damping layers with the relatively high damping values notedherein is located no closer to the outside surface of the diaphragm than25% the distance between the neutral axis of the diaphragm and theoutside surface that is closest to this damping layer. Anyone skilled instructural analysis will understand what the neutral axis is with regardto bending and how to calculate it. Referring to FIG. 3, the laminateddiaphragm (310) may be comprised of two relatively stiff outer layers(312, 316) and one damping layer (314). In the present construction itis possible (but is not necessary) that the relatively stiff outerlayers have the same elastic modulus. As such and given the differingthicknesses of the layers 312 and 316 it becomes clear that the neutralaxis of the diaphragm 315 is not contained within the damping layer 314.Nonetheless, so long as distance (d2) between the centerline 313 of thedamping layer and the outside of the thinner outer layer (316 as drawn)is at least 25% of the distance (d1) between the neutral axis (315) andthe outer surface of the thinner outer layer (316 as shown) then thelaminated diaphragm 310 may still appreciably benefit from theconstrained layer construction.

While there is no fundamental limit to the thickness of the dampinglayer, the upper limit of the thickness of the damping layer mayultimately become a function of the ratio of the moduli between thenon-damping layers and the damping layer, the thickness ratio of thenon-damping layers versus the damping layer, the placement of thedamping layer with respect to the neutral axis of the laminate, thefrequency of interest and the temperature range of interest. In generalthere may be two trends with respect to thickness of the damping layer.The laminate damping gets better with a thicker damping layer. For arelatively stiff damping layer, when compared to the outer layers, theentire laminate may improve in flexural stiffness as the center dampinglayer increases in thickness. However if the damping layer issubstantially lower modulus than the outer stiff layers then it may besaid that the flexural modulus initially improves with damping layerthickness until it reaches a maximum and then it decreases. In theproper proportions damping may be achieved without a substantial loss oreven with a small increase in composite flexural stiffness of thediaphragm. Moreover, cost and space considerations may also contributeto the final thickness selection. The thickness of the damping layer(s)with the relatively high damping values herein preferably is in therange of 1 μm to 200 μm, including all values therein, in 1.0 μmincrements. One preferred range is 1.0 μm to 100 μm.

For the diaphragm depicted in FIG. 2 there is no fundamental limit forthe peel strength that the damping layer (214) which is adhering to theoptical films (212) and (216) provides. In one preferred implementationa permanent adhesive is used with a peel strength of greater than orequal to 3 N/inch. In another preferred implementation a removableadhesive is used with a peel strength of less than 3 N/inch. The peelstrength may also be in the range of 0.005 N/inch to 500 N/inch. Peelstrength may be measured at room temperature using tensile testingapparatus at a peeling angle of 90 degrees and a peeling speed of 300mm/minute.

The lamination may be conducted with multiple production processesincluding roll-to-roll lamination by a machine or lamination by hand.The damping layer(s) with the relatively high damping values may beapplied to the optically clear film(s) in multiple ways includingdispensing or screen printing on one or both sides of one or severaloptically clear films that are to be laminated, it can be applied as aseparate roll of material, it can be applied to one or both opticalfilms prior to the lamination step or during the lamination step or insome other way. Furthermore, the damping layer(s) with the relativelyhigh damping values can be fixated to the films with UV light, heat,pressure or other means. The lamination can be a single step or amulti-step lamination, and may employ heat and/or pressure such as maybe available in typical heated compression mold. The lamination may alsooccur after at least one of the optically clear films has already beenmounted to the transducer frame. It also may be useful during thelamination process to monitor and ensure the optical quality of thediaphragm by minimizing the frequency and size of inclusions, bubbles,scratches and other optical disturbances. Furthermore, it may be usefulto ensure that the diaphragm is resistant to heat and humidity so thatthat diaphragm performance and optical quality is not compromised by thelamination procedure or during its use in a transducer.

The surface of the diaphragm that faces towards the viewer maypreferentially be configured to have a requisite hardness that may thenimprove its use with a given mechanical-to-acoustical transducer over agiven period of time. Accordingly, it may be useful to configure thediaphragm to have a pencil hardness (measured according to JIS K5600-5-4:1999) of greater than or equal to 1H, more preferably greaterthan or equal to 2H. The pencil hardness may also be in the range of 1Hto 9H. The surface hardness may be achieved either through theproperties of the optical film itself or through a coating or othersuitable surface treatment.

Throughout this disclosure there is reference to the feature ofoptically clear film layers and optically clear damping layers. This maybe understood as reference to either a desired haze and/or totalluminous transmittance property for the film and/or damping layer. Thatis, in order for the image of the video display to be visible thediaphragm may be configured to possess a preferable haze and totalluminous transmittance characteristic. For example, the diaphragm mayutilize optically clear film or damping layers having haze values(measured according to ASTM D1003-07e1) of less than or equal to 30%,more preferably less than or equal to 20%. In the case where noantiglare treatment of the diaphragm is desired the haze value ispreferably at or below 4%, more preferably at or below 3% and mostpreferably at or below 2%. The total luminous transmittance propertiesof the optically clear film(s) or damping layer(s) (measured accordingto ASTM D1003-07e1) may be at or above 75%. In the case where noantireflective treatment of the diaphragm is desired the luminoustransmittance properties may more preferably be at or above 80%. Allvalues refer to the properties as measured during or immediately afterproduction of the transducer. That is, the properties are best measuredunder those circumstances where a film is not subject to environmentalchanges (e.g. relatively long term exposure to elevated temperatures)that would alter the referenced haze values and/or luminoustransmittance properties.

In case some of the materials used as all or part of the diaphragmexhibit heat shrinkage, the heat shrinkage is preferably less than orequal to 0.5% in the machine direction (MD) as well as in the transversedirection (TD), where MD and TD are illustrated in FIG. 4. Even morepreferably the shrinkage is at or below 0.2%. Shrinkage may be measuredfor an unrestrained film that has been exposed to 150° C. for 30 min andallowed to cool to room temperature. Alternatively, shrinkage may bemeasured using thermomechanical analysis (with same temperature range)using the appropriate test equipment (example: Perkin Elmer TMA-7).

The optically clear films as well as damping layers used as part of thediaphragm can be treated on none, one or both sides of the film surfacefor improved adhesion of adhesives, to change their surface tension orto impart other desirable properties. One example of an optically clearfilm of this type is DuPont Teijin ST730. It possesses a haze value of1.0% to 1.2% (depending on thickness used), a heat shrinkage value of0.1% both in MD and TD (measured unrestrained at 150° C./30 min) and atotal luminous transmittance of approximately 87%. The material istreated for better adhesion on both surfaces.

In one preferred implementation of a diaphragm for a transducer for a24″ class LCD display and intended for use in a computer monitor,all-in-one PC or TV the following materials can be used to construct thediaphragm: bi-axially stretched, optically clear PET film with 250 μmthickness (DuPont Teijin ST730, available from DuPont Teijin Films U.S,Hopewell, Va.) and a 25 μm thick optically clear acrylic pressuresensitive adhesive (PSA) such as 3M 8211, 3M 8141 (both: 3M Corporation,St. Paul, Minn.) or ARclear 8154 (Adhesives Research, Glen Rock, Pa.).When paired in a sandwich of 250 μm PET, 25 μm PSA, and 250 μm PET, thedamping of the resulting diaphragm will increase by more than a factorof 1.5 over that of the PET material in the region of 500 to 2000 Hz at30° C. As a result the frequency response of the transducer will besignificantly smoother. FIG. 5 shows the damping benefits of thispreferred implementation of a diaphragm for a 24″ class audio transducerwhere 3M 8141 PSA (pressure sensitive adhesive) was used as the dampinglayer for this measurement. Furthermore, FIG. 5 also shows theperformance of the same audio transducer with a different diaphragm. Inthis different diaphragm the 25 μm layer of 3M 8141 PSA has beenreplaced by a layer of a relatively stiffer adhesive (Norland NOA61, UVcured, thickness of adhesive layer is approximately 25 μm, E isapproximately 1.0 GPa). It can be seen in FIG. 5 that in the range of500 Hz to 2000 Hz the peaks in the frequency response are smoothed forthe 3M 8141 PSA implementation relative to the Norland NOA61implementation making the 3M 8141 PSA implementation preferrable.Moreover it can be seen that the additional relative stiffness of the UVadhesive does not impart a significant increase in the level of acousticoutput. Furthermore, FIG. 6 shows the damping benefits of the preferredimplementation of a diaphragm for the 24″ class transducer using adamping layer of an acrylic based pressure sensitive adhesive relativeto a monolithic optically clear polycarbonate membrane of 500 μmthickness (no lamination and no adhesive involved). Again, it can beseen that in the range of 500 Hz to 2000 Hz the peaks in the frequencyresponse in FIG. 6 are smoothed for such preferred implementationrelative to the polycarbonate diaphragm.

Optically clear acrylic based pressure sensitive adhesives suitable foruse as the damping layer herein typically have a damping value tan delta6 in the range of 0.2 to 2 at a temperature of 30° C. and at a frequencyrange of 500 to 2000 Hz, though material with higher or lower values maybe available and may be used as well. The specific value depends onmaterial composition, temperature and frequency. Furthermore, theelastic modulus of such acrylic based pressure sensitive adhesives istypically less than or equal to 2% of the value of biaxially stretchedPET at a temperature of 30° C. and at a frequency range of 500 to 2000Hz.

The coefficient of linear thermal expansion (CLTE) for the film materialfor the diaphragm may have a CLTE in the machine direction (MD) that issubstantially the same as the CLTE in the transverse direction (TD).More specifically, the CLTE for the MD and TD may be within +/−3 μm/m/°C. of one another. The CLTE for the film material may be at or below 50μm/m/° C. Furthermore, it is contemplated that the CLTE for the filmsmay be in the range of 1 μm/m/° C. to 50 μm/m/° C., including all valuestherein, in 1.0 μm/m/° C. increments. CLTE may be measured according toASTM E831-06 and the values listed in this filing are intended to referto a temperature range of 20° C. to 50° C. unless stated otherwise.

Typically, at least one of the optically clear films may be coated onthe outside with an optically clear hardcoat (for example Terapin G fromTekra, New Berlin, Wis.) or with an optically clear anti-glare coating(for example Terapin AG from Tekra). Other coatings that can be appliedcan include but are not limited to antireflective coatings (preferablyapplied in a wet coating process), antistatic coating, anti-smudgecoating, conductive or other suitable coating. Furthermore a reflectionprevention processing, sticking prevention layer, antiglare preventionsurface, etc. may be prepared as part of the optically clear filmitself. Some or all of the surfaces of the individual film and thefinished diaphragm may be protected with a masking film before, duringand/or after the lamination process.

Although each optically clear film material that forms the diaphragm maybe of the same material and may be of materials of different type (e.g.different material or polymeric composition) it is preferable that atleast the two outside layers are in fact chemically similar. Forexample, in the case of polymeric material, it is preferable that thetwo outside layers have the same repeating unit structure, or at aminimum, share the same repeating unit structure while having some otherdissimilar repeating units within the polymer network (e.g. copolymersthat have at least one repeating unit structure in common).

Attention is next directed to FIG. 7 which illustrates yet anotherembodiment of the present invention. As can be seen, shown generally at710 is a diaphragm which contains three optically clear films at 716,718 and 712. Two optically clear adhesive layers are illustrated at 714and 720. The centerline of the diaphragm is shown at 715.

It may therefore be appreciated that there may be situations where thethickness of the three films may all vary, such as the situation whereone may wish to employ an outer layer that contains a specific coatingor which contains a desired surface processing, and which layer is onlyavailable at a relatively reduced thickness. For example, this may bethe situation when one may wish to provide an outer film layer whichcontains an antireflective coating. Optically clear films withantireflective coatings may generally be available at thickness between40 μm to 175 μm, including all values therein, in 1.0 μm increments. Forexample, one may source an optically clear film with an antireflectivecoating that has a thickness of 100 μm.

As may now be appreciated, the desired diaphragm thickness and dampingcharacteristics may be achieved by laminating in the manner noted above,and as generally illustrated in FIG. 7. Furthermore, at least one of thelayers of adhesive may provide a damping tan delta of 0.1 or more in thefrequency range from 500 Hz to 2000 Hz at 30° C.

Expanding upon the above, in one preferred implementation of a diaphragmwith antireflection properties for a transducer for a 24″ class LCDdisplay and intended for use in a computer monitor, all-in-one PC or TV,a sandwich of 250 μm PET, 25 μm PSA, 175 μm PET, 25 μm PSA and 100 μmPET (as the outer layer) with an antireflective coating may be used. Forthe PET with antireflection coating the ReaLook film in the grade 9108from Nippon Oil and Fat (NOF Corporation, Tokyo, Japan) may be used.ReaLook9108 grade is available with a 25 μm PSA already pre-applied. Forthe other two PET layers Dupont Teijin ST730 may be used and for theremaining PSA layer 3M 8211 or Adhesives Research ARclear 8154 may beemployed.

In another preferred implementation of a diaphragm consisting of threeoptically clear films such diaphragm may be configured such that bothouter layers have a relatively higher elastic modulus than the middlelayer of the diaphragm laminate. For example, optically clearpolymethylpentene (tradename TPX) is an extremely light material withdensity in the range of 830 kg/m³ and damping on the order of δ˜0.08(measured at 25 C, 200 Hz). Polymethylpentene material has a relativelylow elastic modulus generally below 2 GPa. Thus while it is lessdesirable as a monolithic material it may be employed to provideadditional damping to the diaphragm (in addition to the dampinglayer(s)) and to reduce the composite density of the diaphragm. In onepreferred implementation polymethylpentene is placed between tworelatively stiff outer layers, selected from acrylates (e.g. poly(methylmethacrylates), aromatic polyesters (e.g. PET) and/or poly(ethylenenaphthalate) (PEN) and these three film layers are laminated togetherwith two 25 μm thick layers of PSA or some other highly damped and softadhesive. These outer layer materials are substantially stiffer but alsohave correspondingly higher density. In this combination the diaphragmcomposite will possess a very high ratio between flexural stiffness anddensity as well as good damping which ultimately will provide goodcharacteristics for use in the mechanical-to-acoustical transducer asnoted above.

In another implementation a diaphragm is constructed that contains atleast one optically clear film, at least one damping layer and at leastone film that is a light polarizing film. There may be several reasonswhy one may want to add a polarizing film to the diaphragm. For examplethe polarizing film may be applied in order to replace the outwardfacing polarizing film of a video display (for example a liquid crystaldisplay panel) in order to reduce the overall cost of the video displayand the diaphragm. Another reason might be to provide for contrastenhancement and glare reduction by suppressing internal reflections fromexternal ambient light (usually in combination with a quarter waveretarder film).

The polarizing film may consist of just a polarizer material or it maybe a laminate of multiple films such as a polarizing material withlayers of protective film on one or both sides and/or a polarizingmaterial in conjunction with a retarder film. The polarizationorientation of the film may be matched with the orientation of the lightemitted from the underlying video display in order to provide formaximum light transmittance. However, it should be noted that the totalluminous transmittance of the polarizing film is lower than foroptically clear film due to its polarizing nature. In one preferredimplementation the total luminous transmittance of the polarizing filmis greater than or equal to 40%. One example of an implementation is theuse of a 250 um PET film such as DuPont ST730 and a 190 um polarizingfilm such as NPF-SEG1224DU (available from Nitto Denko, Tokyo, Japan).The polarizing film comes with a PSA of 25 um applied. When assembled asa transducer and used with a video display the diaphragm is oriented insuch a way that the PET film is facing to the outside (towards theviewer) and the polarizer is facing towards the video display. The PSAlayer of the polarizer represents the damping layer.

In another implementation a diaphragm is constructed that consists of atleast two optically clear films, at least one damping layer and at leastone layer that enables the diaphragm to act as a touch screen. Thephysical principle of this touch screen functionality is not limited toany specific principle. Examples for touch screen technologies thatmight be supported by the diaphragm include capacitive, resistive,surface acoustic wave, optical and infrared touch screens. Examples forone or several layers that enables the diaphragm to act as a touchscreen may be a conductive layer made of ITO material or conductivepolymers.

Frame And Diaphragms With Substantially Matched CLTE

The ability to minimize the thickness of a transducer frame may beimportant for some applications of the above referenced acoustictransducers that are coupled to an edge of a given diaphragm. In theseapplications a relatively thin frame may be desired for visual andaesthetic reasons. In order to achieve a given stiffness of a frame withthe minimum thickness of material and otherwise fixed design constraintsone may select a frame material with relatively high elastic modulussuch as a metal or a reinforced (filled) polymer whereas the diaphragmis generally an optically clear, unfilled polymer. In general metals andreinforced polymers have a substantially lower coefficient of linearthermal expansion than optically clear, unfilled polymers. In generalthe CLTE of metals and certain reinforced polymers can be in the rangefrom 5-35 μm/m/° C. and the CLTE of optically clear polymers will rangefrom 50-200 μm/m/° C.

This mismatch in the CLTE of frame and diaphragm may cause undesirableoptical reflections. An example for a CLTE mismatch in a practicalimplementation occurs when a flat panel TV with an integrated opticallyclear acoustic transducer is turned on and subsequently the video panelsheats up to its operating temperature. The heat generated by theoperation of the video panel is radiated into the surrounding air, someof which is trapped between the video panel and the transducer diaphragmand transducer frame. In turn this air heats up the diaphragm and theframe and causes them to expand. In addition, there can also be directthermal conduction from the video panel into the frame and diaphragm.The CLTE mismatch of diaphragm and frame may cause the diaphragm toexpand at a higher rate then the frame when exposed to a temperaturerise. This in turn causes the diaphragm to change its shape away fromits intended, ideal shape. The change in shape can happen in a multitudeof ways. Examples are a changed diaphragm where the general shape of thecurve of the diaphragm remains however the chord height of the arc ofthe curve is increased, or a diaphragm with a different curve shape suchas multiple areas of waviness or dimples of the diaphragm orcombinations thereof. This change in shape may negatively impact theacoustic performance by changing the acoustic frequency response.Furthermore, such a change in shape may cause optical disturbance forexample in the form of additional, unwanted optical reflections.

There is thus a need for a diaphragm/mechanical-to-acoustical transducerwhich is coupled at the edge of the diaphragm that possesses desirableacoustical performance properties and that at the same time exhibits arelatively low CLTE in order to enable the transducer frame to be maderelatively thin.

Accordingly, in yet another embodiment designed to optimize theperformance of a mechanical-to-acoustical transducer, and in thosesituations where acoustical performance may not be as critical (i.e.utilizing damped layer(s) with relative high degree of damping as notedabove) one may desire to provide a diaphragm configuration that willoptimize the CLTE of the diaphragm to that of a givenmechanical-to-acoustical transducer support frame. Accordingly, one mayoptionally elect not to incorporate one or more damping layers, as notedabove.

Accordingly, various types of optically clear film can be used in suchembodiment, optionally with a damping layer, as long as they exhibit aCLTE of less than or equal to 50 μm/m/° C. in one or both of the machinedirection (MD) or transverse direction (TD). Such CLTE value maytherefore be, e.g. less than or equal to 40 μm/m/° C., or less than orequal to 35 μm/m/° C. One method to achieve said CLTE properties incombination with optical clarity can be achieved by bi-axiallystretching polymeric film. For example, bi-axially stretched PET andPEN, polyester copolymers of PET and PEN, copolymers comprising morethan 70% by weight of either PET or PEN, and polymer blends formed bycombination of suitable polymers providing that the blend exhibitsorientation characteristics typical of PET and PEN during the filmforming process can be used. Furthermore, biaxially stretched celluloseacetate (CA) may be used, specifically cellulose diacetate or cellulosetriacetate, which substituted cellulosic materials may also includevarious additives such as plasticizers and other relatively lowmolecular weight compounds. Additionally this embodiment contemplatesthe use of a relatively stiffer optically clear fibers of matched indexof refraction to the materials used for the optically clear films, suchthat they may contribute to relative stiffness while reducing therelative amount of thermal expansion.

The lamination that may be utilized herein is not limited to anyspecific method. For example, one may use heat and/or pressure. It isuseful to control the lamination procedure such that one provides theoptical clarity noted herein (i.e. haze values of less than or equal to30% and/or total luminous transmittance properties of the opticallyclear film(s) or damping layer(s) may be at or above 75%). In onepreferred implementation a relatively thin layer of UV cured adhesiveand a roll-to-roll lamination process are used because they are a verycost effective lamination method.

In yet another preferred implementation of a diaphragm for a transducerfor a 24″ class LCD display and intended for use in a computer monitor,all-in-one PC or TV the following materials can be used to construct thediaphragm: two bi-axially stretched, optically clear PET films with 250μm thickness each (DuPont Teijin ST730) and one optically clear UV curedamping adhesive layer (Norland Products Adhesive #61, thickness ofadhesive layer is approximately 25 μm). Such film has a CLTE of 19μm/m/° C. (in the temperature range of 20° C.-50° C.). The resultingdiaphragm also has a composite CLTE of approximately 19 μm/m/° C. (inthe temperature range of 20° C.-50° C.). In a preferred implementationsuch diaphragm may used in conjunction with a transducer frame whichfour sides are made primarily of aluminum with a typical CLTE of 22μm/m/° C. The resulting mismatch of CLTE is minimized to approximately 3μm/m/° C.

It can be seen in FIG. 8 that for the frequency range of 500 Hz to 2000Hz the smoothness of the frequency response of this construction iscomparable to the one obtained with a 500 μm thick diaphragm made ofmonolithic polycarbonate. However, polycarbonate has a CLTE of typically70 μm/m/° C. which results in a CLTE mismatch to the desired aluminumframe construction of approximately 48 μm/m/° C. in both in-planedimensions of the diaphragm. It should be noted that a damped adhesivelayer such as 25 μm of acrylic pressure sensitive adhesive may be usedas well. However, as noted above, in this embodiment, it is not requiredto use a damping layer, and one may simply utilize an adhesive or anyother lamination method which does not amount to a damping layer havinga damping value tan delta of more than 0.1. Said adhesive or laminationmethod may result in a thickness of the lamination layer of more or lessthan 25 um.

Furthermore, the production cost of such a diaphragm may be relativelylower than for a diaphragm containing a damping layer which might makesuch a preferable optional construction. Furthermore, other aspects of adiaphragm without a damping layer might be preferable over a diaphragmcontaining a damping layer—for example the resistance of the laminationto heat and humidity. One may appreciate that this concept can beextended to laminates of more than two optically clear films and morethan one damping layer as long as the composite in-plane CLTE of thediaphragm is within the desired range.

FIG. 9 depicts another embodiment where a diaphragm is constructed withan orthotropic CLTE and where such diaphragm may be paired with a hybridframe construction that has a similar difference in its CLTE. Bi-axiallystretched polyester type polymers may exhibit orthotropic materialproperties. For example PET and PEN films can be produced to have a CLTEof 30 μm/m/° C. in the machine direction (MD) and only 20 μm/m/° C. inthe tension direction (TD). As therefore shown in FIG. 4, the CLTEmaxima or minima may not perfectly align with the machine direction (MD)nor the tension direction (TD). Nonetheless for the purpose of economicuse of films in roll form it may be preferable to orient cutting ofrectangular sheets in directions aligned with the roll direction (MD).As such, reference to orthotropic properties means that whatever theorientation of how the sheet was cut from the roll, the materialproperties (for example E and CTLE) may vary in 2 orthogonal directionsof the resulting cut rectangular sheet.

As such it is possible to utilize this property to build a hybridtransducer frame where the members aligned with the diaphragm MD mayhave a substantially different CLTE than those frame members aligned inthe diaphragm TD direction and at the same time maintain a minimum CLTEmismatch in 2 directions. One preferred implementation is a rectangulartransducer frame constructed from aluminum side rails with a CLTE of 22μm/m/° C. and glass re-inforced ABS with a CLTE of approximately 35μm/m/° C.

Shown in FIG. 9 is such an assembly, the frame members (952) generallyaligned in the y direction are constructed from material y and framemembers (953) generally aligned in the x direction are constructed frommaterial x. The orthotropic diaphragm (910) has CLTE properties suchthat in the x direction it is generally close to the CLTE of (953) framematerial x and in the y direction it is generally close to the CLTE of(952) frame material y. As previously discussed the preferredimplementation in each direction is that the CLTE mismatch for bothin-plane dimensions of the diaphragm should be no greater than 20 μm/m/°C., more preferably no greater than 10 μm/m/° C. and most preferably nogreater than 5 μm/m/° C.

Shown in FIG. 10 is an alternate construction of the diaphragm laminate(1010). It can be constructed such that the orientation of theorthotropic layers are alternated in such a way to reduce anisotropicityin the plane. Ultimately this may produce a laminate that is moreisotropic in plane and thus a transducer frame may be constructed out ofmaterials with the same CLTE for all components and still maintain aminimum mismatch of CTLE.

In another lamination strategy, the change of the CLTE with regard tothickness the base material may be exploited to reduce the overall CLTEof the laminate. For example biaxially stretched PET is known to exhibitthis phenomenon in some cases (see FIG. 11). When for example a laminateis constructed from three sheets of 175 μm thickness instead of twosheets of 250 μm thickness then the overall laminate CLTE may be reducedfor a construction of nearly the same overall thickness.

FIG. 12 depicts yet another embodiment where the orthotropic E of thebi-axially stretched polymer diaphragm (1210) may be used to tune thesystem to separate component resonances. Bi-axially stretched polyestertype polymers exhibit largely orthotropic material properties. Forexample optically clear PET films may have a tensile modulus E=3.0 GPain the machine direction (MD) and E=4.0 GPa in the tension direction(TD)—see FIG. 4. This is a process variable related to the stretch ratioand is only shown as one example. The orientation of the stifferdirection of the film has direct impact on the acoustic output ofspeakers. At least one of these speaker designs is such that 2 sides(1252) of a rectangular frame are driven by piezo actuators mounted inthe transducer frame and 2 sides (1253) of the diaphragm are mounted bysome means passively to the frame. As such the predominant production ofundesirable acoustic modes emanate in the direction that runs betweenopposing piezo actuators (direction x as shown in FIG. 12). It is usefulin speaker design to assemble the system such that resonances ofindividual components do not align with resonances from othercomponents. The modulus of elasticity in the x direction contributes tothe resonant frequencies of the diaphragm with the approximateproportion of: ω_(n)∝√{square root over (E_(x))}. Given the large rangeof E from MD to TD, the alignment of MD and TD within diaphragm (1210)with respect to frame members (1252, 1253) has an impact on the resonantfrequencies of the diaphragm between the piezo actuators (in the xdirection). Thus the orthotropic stiffness of the diaphragm presents anopportunity for the designer to redistribute the modal behavior withinthe whole system by simply reorienting how the diaphragm is cut off theroll of the film. Thus this is a further feature of the presentinvention.

Various embodiment of the present invention have been presented hereinrelating to a diaphragm that may be employed with amechanical-to-acoustical transducer. It should therefore be understoodthat all of the various features amongst the various embodiments may beexchanged to either optimize audio performance and/or the ability of thediaphragm/transducer to accommodate various operational and/orenvironmental conditions, such that any one embodiment herein mayinclude any one or more of the various features described above.

The invention claimed is:
 1. A device that converts a mechanical motioninto acoustic energy, the device comprising: a multi-layer diaphragm,wherein at least one of the layers is a damping layer that is positionedbetween two other layers; at least one support; and at least onemechanical-to-acoustical transducer including a distal portion coupledto the diaphragm and a proximal portion coupled to the support, whereinmovement of the transducer causes movement of the diaphragm in adirection that is generally transverse to the direction of the movementof the transducer.
 2. The device according to claim 1, wherein thediaphragm is an optically clear diaphragm.
 3. The device according toclaim 2, wherein the diaphragm comprises first and second opticallyclear layers.
 4. The device according to claim 3, wherein the diaphragmis configured such that the damping layer is between the first andsecond optically clear layers.
 5. The device of claim 3, wherein saiddamping layer is an adhesive and one of the optically clear layers isadhered to the damping layer with a peel strength of greater than orequal to 0.005 N/inch.
 6. The device according to claim 1, wherein thediaphragm and the support comprise substantially the same coefficient oflinear thermal expansion.
 7. The device of claim 1, wherein saiddiaphragm has a damping value of tan delta equal to or greater than 0.06in the frequency range of 500 Hz to 2000 Hz at 30° C.
 8. The device ofclaim 1, wherein said diaphragm has a damping value of tan delta equalto or greater than 0.08 in the frequency range of 500 Hz to 2000 Hz at30° C.
 9. The device of claim 1, where the thickness of the dampinglayer is in the range of 1 μm to 200 μm.
 10. The device of claim 1,wherein the diaphragm has a composite modulus of equal to or greaterthan 2.0 GPa.
 11. A device that converts a mechanical motion intoacoustic energy, the device comprising: a curved multi-layer diaphragm,wherein at least one of the layers is a damping layer that is positionedbetween two other layers; at least one support; and at least onemechanical-to-acoustical transducer including a distal portion coupledto the diaphragm and a proximal portion coupled to the support, whereinmovement of the transducer causes movement of the diaphragm in adirection that is generally transverse to the direction of the movementof the transducer.
 12. The device according to claim 11, wherein thediaphragm comprises first and second optically clear layers.
 13. Thedevice according to claim 12, wherein the diaphragm is configured suchthat the damping layer is between the first and second optically clearlayers.
 14. The device of claim 13, wherein said damping layer is anadhesive and one of the optically clear layers is adhered to the dampinglayer with a peel strength of greater than or equal to 0.005 N/inch. 15.The device according to claim 11, wherein the diaphragm and the supportcomprise substantially the same coefficient of linear thermal expansion.16. The device of claim 11, wherein said diaphragm has a damping valueof tan delta equal to or greater than 0.06 in the frequency range of 500Hz to 2000 Hz at 30° C.
 17. The device of claim 11, wherein saiddiaphragm has a damping value of tan delta equal to or greater than 0.08in the frequency range of 500 Hz to 2000 Hz at 30° C.
 18. The device ofclaim 11, where the thickness of the damping layer is in the range of 1μm to 200 μm.
 19. The device of claim 11, wherein the diaphragm has acomposite modulus of equal to or greater than 2.0 GPa.
 20. A device thatconverts a mechanical motion into acoustic energy, the devicecomprising: a multi-layer diaphragm, wherein at least one of the layersfunctions as both an adhesive and a damping layer that is positionedbetween two other layers; at least one support; and at least onemechanical-to-acoustical transducer including a distal portion coupledto the diaphragm and a proximal portion coupled to the support, whereinmovement of the transducer causes movement of the diaphragm in adirection that is generally transverse to the direction of the movementof the transducer.
 21. The device according to claim 20, wherein thediaphragm is an optically clear diaphragm.
 22. The device according toclaim 21, wherein the diaphragm comprises first and second opticallyclear layers.
 23. The device according to claim 22, wherein thediaphragm is configured such that the damping layer is between the firstand second optically clear layers.
 24. The device according to claim 20,wherein the diaphragm and the support comprise substantially the samecoefficient of linear thermal expansion.